An ion channel is a pore formed by one or more protein subunits in the cell membrane. This pore allows the diffusion of substances into (influx) and/or out of (efflux) the cell. These substances are usually ions or lipid-soluble molecules. Sodium channels are commonly found in nerve cells in the brain and spinal cord, and in skeletal muscle cells where sodium channel expression is high. Ion channels are distinct in many ways and have been characterized through advances in molecular biology and classified according to pharmacological and biophysical properties. Studies have revealed the selectivity of each class of ion channel, allowing certain ions to pass through. For example, potassium ions are very similar to sodium ions, but the potassium ions cannot pass through many sodium channels. Such distinguishing features are advantageous when developing methodologies to study these unique proteins.
Ion channels have many distinct biophysical functions. Sodium channels play a very important role in the propagation of action potentials in excitatory cells which function in such important processes as sensory perception. Disorders associated with abnormal sodium channel function include epilepsy and seizures, cardiac arrhythmias, mental illness, neuroma tumors (tumors derived from cells of the nervous system), various myotonias (types of myopathies with excessive muscle rigidity or contractions), hyper- and hypo-kalemic paralysis (types of myopathies with episodes of flaccid paralysis or weakness), hypothyroidism (under activity of the thyroid gland, which produces iodine hormones), various neuropathies (diseases of peripheral nerves, causing weakness or numbness), and allodynia and hyperaesthesia (both forms of hyper excitability, where sharp, shooting pain results from normally innocuous sensory stimuli, such as touch). Due to this wide range of disorders that are associated with sodium channels, pharmaceutical, medical, and biological research has focused their efforts to find drug candidates to treat and prevent sodium channel-related diseases.
Traditionally, analytical applications for ion channel analysis have fallen on either of the extremes of accuracy or speed. The patch-clamp method is indisputably the most accurate, but it has a low throughput speed. Fluorescent dye measurements offer unsurpassed analysis speed, but suffer from low accuracy. Furthermore, other techniques that manage to sit in the middle ground between high accuracy and fast speed do possess equally limited disadvantages. The radioactive 86Rb+ efflux assay, for example, is a relatively unsafe and inconvenient technique in that the radioactive isotopes required are harmful to human operators, the half-life of the isotopes restricts the time duration of experiments, and there are radioactive waste disposal considerations to be dealt with. All of the techniques described above are an indirect measure of intracellular ion concentration. Accordingly it is an object of this invention to provide a method for preparing and analyzing sample cell cultures for ion channel activity such that a direct and accurate measurement of intracellular ion concentration may be achieved.
The present invention pertains to experimental methodologies for biopharmaceutical research, particularly for the analysis of drug candidates for therapeutic effects on ion channels. The invention describes a method of preparing sample cell cultures for analysis, and using a unique flux assay and the techniques of flame atomic absorption spectrometry (FAAS) or graphite furnace atomic absorption spectrometry (GFAAS) to directly measure the intracellular ion content of those cell cultures, enabling the measurement of ion flux and ion channel activity.
An advantage of this invention is that the experimental methodology described herein provides a way for researchers to accurately determine the therapeutic effects of candidate compounds for sodium channel drug discovery.